Copper foil is widely used as a material for forming printed wiring boards. A printed wiring board is obtained from bonding copper foil and other kinds of materials, such as a pre-preg. SO, higher adhesion is required between copper foil and a pre-preg or the like.
As one of the methods for increasing the adhesion between copper foil and a pre-preg or the like, nodules are formed to have a roughness Rz of several micrometers when measured by a stylus-type roughness meter, for example. As such, a matte surface and/or a shiny surface of untreated copper foil is subjected to nodular treatment to have a nodular surface, whereby surface-treated copper foil is formed from the untreated copper foil. Then the anchoring effect of the nodular surface on a pre-preg or the like is performed. And the anchoring effect is caused by the embedding of nodules in a pre-preg or the like. So, it is generally understood that the adhesion between a nodular surface of copper foil and a pre-preg or the like increases with an increase in the size of nodules on the copper foil, and eventually with the above-described roughness Rz of a nodular surface. For this reason, to estimate the adhesion between a nodular surface of copper foil and a pre-preg or the like, the degree of nodular treatment has hitherto been evaluated by the roughness Rz measured by a stylus-type roughness mater and the like as specified in IPC TM650 Section 2.2.17A. Then the adhesion between a nodular surface of copper foil and a pre-preg or the like has been estimated by this roughness Rz and the like.
However, depending on the shape of nodules on a nodular surface of copper foil after nodular treatment, there is sometime miss matching in relationship within an increase in the roughness Rz measured by the above-described stylus-type roughness meter and an increase in the adhesion of the above-described nodular surface of copper foil. That is, even when the roughness Rz measured by a stylus-type roughness meter on a nodular surface of copper foil is substantially at the same level in surface-treated copper foil, when the shape of nodules and the like are different, the adhesion is not substantially at the same level and variations are found in the adhesion.
Incidentally, it is required on recent printed wiring boards, especially in multilayer printed wiring boards to be thinner than ever. For this reason, also for copper foil which is a material for printed wiring boards, thinner surface-treated copper foil is required and besides, smaller nodules on a nodular surface of the copper foil, that is, lower the above-described roughness Rz. For example, when the above-described roughness Rz of a nodular surface of surface-treated copper foil caused by higher nodular treatment, it is not recommended because it worsen both the electric properties of a circuit formed from this copper foils and the formability of fine circuits.
However, as described above, the adhesion of a nodular surface of copper foil may sometimes show variations even when the roughness Rz measured by a stylus-type roughness meter is substantially at the same level. Therefore, it has been necessary to set the minimum value of the above-described roughness Rz of a nodular surface of copper foil at somewhat high levels when importance is attached to ensuring a prescribed adhesion. This is the reason why the above-described roughness Rz of a nodular surface of copper foil cannot be set at very low levels.
In this connection, Patent Document 1 (Japanese Patent Laid-Open No. H10-265991) discloses a plated material excellent in resin adhesion, in which a coating layer of Cu and the like is formed on the surface of a metal sheet. This coated material is such that when the surface of the coated material is measured in magnification of 3000 times by an electron beam three-dimensional roughness analyzer, the arithmetic average roughness (Ra) is 0.03 to 0.5 μm and the surface-area alternative value which is defined as (surface area of a sample obtained from measurement)/(measured area in two dimension) is 1.01 to 1.1. In this invention, the problem to be solved is to supply a metal material which has adhesion to resin by keeping the arithmetic average roughness (Ra) and the surface-area alternative value in appropriate ranges.
[Patent Document 1]: Japanese Patent Laid-Open No. H10-265991 (page 2, first column)